The invention relates to irradiated articles molded from thermoplastic molding compositions and more particularly relates to articles molded from compositions of blended aromatic polycarbonate resins and polyamide resins, sterilized by ionizing radiation.
Synthetic polymeric resins have been used increasingly to mold articles useful in medicine and surgery. Examples of such articles include containers, packaging, instruments, prosthetics, tubing, and working components of treatment apparatus. the selection of a particular polymeric resin will depend on the physical properties required in the molded article.
One property necessary to many medical and surgical articles molded from thermoplastic polymeric resins, is their receptivity to sterilization procedures. A commonly preferred sterilization technique is exposure to ionizing radiation. Unfortunately, ionizing radiation may adversely impact some polyaeric resins in ways unacceptable to some uses.
For example, polycarbonate resins have many properties which are advantageous to their use in many medical and surgical devices or articles. However, upon exposure to ionizing radiation they change from a normally desired transparency and clarity to a yellowed coloration. In addition, this yellow color formed is unstable and continuously changes with increasing time after gamma ray exposure. Aesthetically, the yellowed coloration and the continuously changing color are not always acceptable.
A number of compounds have been prepared as additives to polycarbonate resins, to inhibit the yellowing of articles molded from polycarbonates and subjected to ionizing radiation. Representative of these additives are those described in the U.S. Pat. Nos. 4,624,972 (Nace); 4,657,949 (Nace); 4,757,104 (Nace); and 4,804,692 (Lundy et al.). However, the presence of any additive on a polycarbonate resin molding composition generally has an effect on other desirable physical properties.
Another strategy for reducing the yellowing of a polycarbonate resin upon exposure to ionizing radiation is described in the U.S. Pat. No. 4,778,656 (Allen et al, 1988). The method entails blending the polymer with another polymer, which has the effect of improving ionizing radiation resistance of the polycarbonate. Examples of the additive polymers are polyester, polysulfone-carbonates and certain copolyesters. Like the previously described yellowing inhibitors, these additive polymers also affect physical properties in articles molded from blends of the mixed polymers. This is not to say that some combinations of polymeric resins are not applicable for molding articles useful in medical and surgical procedures. In fact, blends of polycarbonates and polyamides have gained some interest in other areas because of their unique properties.
Blends of polycarbonate resin and polyamide resin, such as amorphous polyamide, have been found to possess a unique combination of properties which include, for example, high resistance to permeation by gases such as oxygen and carbon dioxide, low water absorption, high creep resistance, and good organic solvent resistance; see for example U.S. Pat. No. 4,749,754 (Gallucci et al, 1988).